I picked up a clean Savage 99A in .308win. It has the internal aluminum magazine. The magazine was pretty sluggish at first but oiling it liberaly and repeated loading/unloading helped.

Only now the third round in the mag sometimes doesn't rotate up. Working the action with authority usually causes it to function but that one round is still sticky enough for me to not trust it's reliability.

I will try some gun scrubber next once I am able to get a can. I don't want to try taking it apart to clean. Any other thoughts?

My suggestion would be to ask the question on the Savage Collectors forum. There are some very knowledgeable Savage aficionados there!

You can increase the magazine spring tension without taking it apart. There should be some YouTube videos on the 99 that will help.

Are you confident the OAL of your cartridges is not too long, and a round is hanging up as the spool rotates?
What is the knowledge of those reading this on the maximum OAL usable on the ".308" length 99 rotary magazines?
Good luck, post what you figure out.
Cheers,
Rex

Messing with the spring is a last resort , so make sure it's not hanging up due to OAL like the previous post, or just stiff from non-use or crud. The spring tension can be increased, but you need to study up on it well before trying. Mine is a bit weak in my .243 from 1966, but as long as it raises the last one into position, I'll leave well enough alone.

Drop down to the Savage Collectors Forum and ask them. They'll tell you way more than you'd ever want to know about it.

Yep, real 99 loonies can no doubt help.

I am only a semi-99 loony, having owned a couple dozen from an 1895 .30-30 to a .284. When I ran into a problem with the rotary magazine on an early tang-safety .250, and couldn't figure it out myself (despite being an OK home-gunsmith) took it to an experienced local smith, who fixed it for $50.

My 99EG in .308 wouldn't cycle the rounds, either, and I needed to increase the spring tension. There's a youtube video on it, and it helped me get mine taken care of:
https://www.youtube.com/watch?v=oXerR6eDwOA

Super easy to adjust the spring tension.

I don't think it's the round itself hanging up. The ammo I've been using is Hornady factory 150gr.

Sounds to me as though it's likely full of old oil and gunk. Been there, suffered that.

MY preference to clean 50 or 100 year old oil and gunk from a Savage 99 action is to remove the stock, then hold the barrel with insulated gloves while pouring boiling water through the action. Removes gunk like magic, and if you pour the boiling water out immediately the action dries almost immediately. Leave the action open for a day to let any remaining droplets dry and proceed from there.

Others prefer to remove all the pieces and clean manually, and then reassemble.

My '52 EG had a semi-stuck magazine. After reading the "you don't want to take it apart stories" I took the stocks off and disassembled the receiver except for the magazine. Then sprayed Gun Scrubber in the magazine and dumped bunch of nasty stuff out the top. Did that twice, blew it out with compressed air. Then sprayed Breakfree in the magazine, let it sit for little while and blew that out with compressed air. That fixed it perfectly, it's been working fine ever since.
I think might work for you too, it's pretty quick and easy. If nothing is broke inside it's worth a try.

There are YouTube videos on how to disassemble and reassemble the 99, if you really need to take it apart to clean it. It isn't that hard. I have taken several apart and reassembled them, and they still work, fancy that!

If a good cleaning doesn't help and you want to try increasing the rotor tension this is a video of me adjusting mine. Still working well.

https://www.youtube.com/watch?v=oXerR6eDwOA

Hey @North61 ! That was a great video--I linked it on page one, as it was VERY helpful to me in adjusting my spring. Thanks for taking the time to film it and upload it.

Sorry to quote my own question but I was just reading Mule Deer's article on the .358 Win in "Gack II" and he implied 2.85 as the magazine length in his old 99F .358 (unless I read that wrong).
I just started loading again for my 99E (aluminum spool, originally a .308, rebarrelled with an original 99 Series A .358 barrel). My first batch is working up in steps to Mule Deer's 200 grain load with 52 grains TAC. 2.82" OAL seats the 200 Barnes TTSX .050" off the lands and 5 of them feed smoothly through the magazine.
Just wanted to add that in case a search leads anyone to the question I posted.
Cheers,
Rex